Experimental study of the Rhone plume. Part I: Physics and dynamics

The complicated dynamic processes occurring when fluvial waters mix with ma rine waters control the nature and the fluxes of materials exported tay riv ers to the sea. Understanding these processes is of primary importance in e valuating budgets. In wide-open estuarine situations these processes take p lace under the influence of an intense turbulence induced by tides. Convers ely, the Rhone waters spread into the Mediterranean Sea in the form of an e asily distinguishable buoyant plume often extending far offshore from the m outh of the river. The aim of this study is to describe the dynamic and hyd rological fields on the basis of eulerian VHF radar mapping of surface curr ents coupled with lagrangian in situ physical or geochemical measurements. This paper focuses mainly on physical processes. Data analysis provides an insight into the typical scales of variability of the phenomena, either ver tically or horizontally. It is shown that morphological fluctuations can oc cur (mainly in orientation and offshore extent) according to wind and outfl ow forcing conditions, and that the vertical structure variations can range from an almost unaltered two-layer distribution to an evolving and deepeni ng mixed layer situation, or even to a more complex superimposed multi-laye red structure. The simultaneous examination of radar maps and lagrangian dr ifter tracking allows the main dynamic tendencies of the Rhone plume to be sketched out. (C) Elsevier, Paris.